Pulmonary circulation

The pulmonary circulatory system is the portion of the cardiovascular system in which oxygen-depletedblood is pumped away from the heart, via thepulmonary artery, to the lungsand returned, oxygenated, to the heart via the pulmonary vein.

Oxygen deprived blood from the vena cava, enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then pumped through thepulmonarysemilunar valve into the pulmonary artery to the lungs. Gas exchange occurs in the lungs, wherebyCO2 is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the heart.

Systemic circulation

Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart, to the rest of the body, and returns oxygen-depleted blood back to the heart. Systemic circulation is, distance-wise, much longer than pulmonary circulation, transporting blood to every part of the body.

View from the front, which means the right side of the heart is on the left of the diagram (and vice-versa)

Heart

The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total:left atrium, left ventricle, right atrium and right ventricle. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

Closed cardiovascular system

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network ofblood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and entersinterstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the lymphatic system, is not closed.

Oxygen transportation

About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with haemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to haemoglobin. The haemoglobin molecule is the primary transporter of oxygen in mammals and many other species.

An animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at real time (20 seconds of cycle) and shows the red blood cell deform as it enters capillaries, as well as changing color as it alternates in states of oxygenation along the circulatory system.

Development

The development of the circulatory system initially occurs by the process of vasculogenesis. The human arterial and venous systems develop from different embryonic areas. While the arterial system develops mainly from the aortic arches, the venous system arises from three bilateral veins during weeks 4 - 8 of human development.

Arterial development

The human arterial system originate from the aortic arches and from the dorsal aortae starting from week 4 of human development. Aortic arch 1 almost completely regresses except to form the maxillary arteries. Aortic arch 2 also completely regresses except to form the stapedial arteries. The definitive formation of the arterial system arise from aortic arches 3, 4 and 6. While aortic arch 5 completely regreses.

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